Methylisothiazolinone (MI): the leave-on ban explained

What MI is, and why it is in the news

Methylisothiazolinone, or MI, is used to keep water-based products free of microbes. It is often used alone or together with methylchloroisothiazolinone (MCI), as MCI/MI. A 2026 study found MCI/MI or MI listed on 257 cosmetic products on the Danish market, mostly shampoos and conditioners.¹

The concern is contact allergy to MI and its mix partner, which the 2026 Danish study found is still common in Europe.¹

What the EU did

Commission Regulation (EU) 2016/1198 amended the EU's list of allowed preservatives. In its recitals it relies on the safety committee's 2013 opinion, which concluded that the existing permitted level, 100 ppm, was not safe, and that for leave-on products, including wet wipes, no safe concentration had been shown. The Commission therefore banned MI from leave-on products, giving industry a transition period.²

Rinse-off products stayed allowed, within limits. MI used alone is allowed in rinse-off products at up to 0.01% (100 ppm),² and the 2026 Danish study refers to a 15 ppm limit for rinse-off products containing the mixture with methylchloroisothiazolinone.¹

Snifff's summary above sets out how this differs in India. The Indian position is Snifff's summary.

Did the rules end the problem?

Not entirely. The 2026 Danish study tested 30 shampoos and liquid soaps. Two of 25 products labelled as containing MCI/MI or MI exceeded the 15 ppm limit, and four did not meet the required 3-to-1 MCI to MI ratio.¹ The authors note that contact allergy to MCI/MI remains common in the EU despite the regulation, and suggest that 15 ppm may be too high to protect people sufficiently.¹

If you know you are allergic, the label is the only reliable defence: look for Methylisothiazolinone and Methylchloroisothiazolinone in the ingredient list of rinse-off products too.

What a US expert panel concluded

Not every safety reviewer reached the EU position. The Cosmetic Ingredient Review expert panel, a US body, reviewed MI in 2019. It concluded MI is safe in rinse-off cosmetics at up to 100 ppm, and safe in leave-on cosmetics only when they are formulated to be nonsensitising, which it said may be determined by a quantitative risk assessment.³ The panel was set up in 1976 by the cosmetics industry’s trade association, with support from the US Food and Drug Administration and the Consumer Federation of America.⁴

The 100 ppm rinse-off figure matches the EU limit for MI used alone,² so the two positions differ mainly on leave-on products, which the EU banned.² The 15 ppm limit in the 2026 Danish study applies to the mixture with methylchloroisothiazolinone.¹ Which rule applies to you depends on where the product is sold.

Using methylisothiazolinone with other products

We did not find a source on combining MI with other ingredients. The relevant point is the one above: MI is commonly paired with MCI.

Methylisothiazolinone in pregnancy and breastfeeding

Evidence on cosmetic products in pregnancy is limited overall, so ask your doctor or midwife about the specific product you use.⁵

What you will see on the label

The names to look for are Methylisothiazolinone and Methylchloroisothiazolinone. In Snifff, it reads as High risk. For the rest of the formula, see what the score means and how to read the list.

As Snifff shows it

Methylisothiazolinone

High risk

Pregnancy and nursing

We found no pregnancy- or lactation-specific evidence for this ingredient.

Regulatory gap

The EU bans methylisothiazolinone in leave-on products, including wet wipes. India permits it as a preservative without the same leave-on ban.

Wording as it appears in the extension, which can change between releases.